Field of the Invention
The present invention relates to a method for assembling a gas sensor including a ceramic sensor element and to an assembly apparatus for use in assembling the same.
Description of the Background Art
A gas sensor including a sensor element formed of oxygen-ion conductive solid electrolyte ceramic such as zirconia (ZrO2) has been conventionally known as a device that measures the concentration of a predetermined gas component of a measurement gas such as an exhaust gas and a combustion gas in an internal combustion engine, usually a car engine.
In such a gas sensor, an elongated-plate-shaped ceramic sensor element (detection element) is usually fixed by a plurality of ceramic supporters which are ceramic insulators glass and by ceramic powder compacts each filled between the ceramic supporters, such as talc, and is hermetically sealed with the powder compacts in a metal housing and a hollow portion of a cylindrical inner tube welded and fixed to the housing. The method and apparatus for preferably assembling such a gas sensor have been known (for example, see WO 2013/005491 and Japanese Patent Application Laid-Open No. 2005-37372).
In the technique disclosed in WO 2013/005491, even when a sensor element warps and a dimensional tolerance between the sensor element and a plurality of members (annular mount members, annular mounting parts) to be annularly mounted is small, the annular mount members (annular mounting parts) can be annularly mounted with reliability.
In the technique disclosed in WO 2013/005491, the annular mount members are annularly mounted to the sensor element from an end at the side at which the opening for introducing a measurement gas into the element is provided. Thus, the application of this technique to a sensor element, whose surface at the side of the relevant end is covered with a protective film (protective layer), is not preferred because the protective film may be damaged or peeled off.
Japanese Patent Application Laid-Open No. 2005-37372 discloses a method for manufacturing a gas sensor including a detection element whose one end side is covered with a protective layer. In the method disclosed in Japanese Patent Application Laid-Open No. 2005-37372, however, a plurality of annular mounting parts are once annularly mounted to a pin member similar in shape to the detection element, the pin member is pulled out so that the plurality of annular mounting parts are stacked, and then the detection element is inserted into the stacked annular mounting parts. Consequently, the annular mounting parts are likely to slide out of place when the pin member is pulled out or the detection element is inserted.